“In the long term, battery technology will not be able to meet the demand being created by the expansion of internet of things (IoT) applications,” James Myers, director of devices and circuits at UK chipmaker Arm’s research and development division. The firm estimates that if each of the trillion or so wireless sensor nodes that are projected used a small lithium coin cell, it would require over 100,000 tonnes of lithium — almost three times the current worldwide annual production.
Batteries have become a big business in recent years due to the demand from the increasing number of mobile devices, electric vehicles, energy storage installations and the IoT. The sensors, connectivity and edge computing that makes up IoT networks require minimal power output, so there have been significant advancements in low-power battery technology. Longer lifetimes and greater dependability are positive steps but one day those batteries will need to be changed, and if you run a smart building or city full of sensors then changing batteries is a serious undertaking.
Myers and many others are part of a movement that hopes to rid us of batteries in low-power applications in order to reduce the cost, risk, and hassle of maintaining those batteries. The logical alternative, they say, is energy harvesting - the process of scavenging ambient power from the local environment. This could be through photosensitive materials to generate solar power, by harnessing kinetic energy through piezoelectric methods, thermoelectric energy from heat, or other similar approaches.
“Energy harvesting is simply a necessity if a large population of IoT devices is to be powered,” Myres told the FT. “There’s certainly an opportunity here to remove batteries and the idea of ‘deploy and forget’ is what’s driving that. It’s not here yet, but it’s the direction in which we’re traveling.”
Energy harvesting is not new. Historians would date the concept back thousands of years to the first windmills and waterwheels of ancient Middle Eastern civilizations. Renewable energy was born from the energy harvesting concept and while giant solar farms may depart from the “local” element of the definition, distributed or rooftop solar realign renewables with energy harvesting somewhat. Today, however, energy harvesting is more often used to describe micro-scale power generation for low-power devices, such as those that make up the IoT.
Ironically, today’s modern windmills, the power generating wind turbine, are pushing the boundaries of micro-scale energy harvesting for the variety of sensors that optimize their operation. Offshore windfarms, for example, suffer from “scour” - the erosion of the seabed around their base - and battery-powered sensors are used to monitor that process to alert underwater maintenance operators when action is required. Those batteries need changing, however, and their location makes that an expensive and dangerous activity.
“Left untreated, scour problems can lead to serious damage and even collapse,” says Jerry Luo of Cranfield University in the UK who is part of a team developing a system to harvest piezoelectric energy from the almost constant vibrations of the turbine’s structure as it is lashed by wind and waves.
This renewable source of power could reduce the need for battery maintenance/change in such challenging environments. “By using energy harvesting, the structural health monitoring system we envisage is economical, self-sustainable and requires minimal intervention,” he told FT.
Another fascinating example of energy harvesting for IoT devices is stealing energy from human movement to power wearable technology. A group of researchers has developed an energy harvester that is attached to the wearer's knee and can generate 1.6 microwatts of power while the person walks without any additional effort. 1.6 microwatts is enough to power small electronics like health monitoring equipment or GPS devices.
“Self-powered equipment can enable users to get rid of the inconvenient daily charge. This energy harvester would promote the development of self-powered wearable devices,” said Wei-Hsin Liao, professor in the department of mechanical and automation engineering and author of a research paper. This and similar technology could give a significant boost for wearables, embedded technology, health monitoring, security and occupant tracking, among other IoT and smart building applications.
Energy harvesting is like distributed renewable energy generation but on a micro-scale for IoT and other low-power devices. Like the decentralization and environmental trends impacting the grid-scale energy system, energy harvesting gathers renewable energy from its environment to rid us of old fashioned technology and provide a range of benefits. In the future, this scalable renewable energy generation may be found in our remote facilities, our sensor-rich smart buildings, and even on or in our bodies.